Which frequency is not used for aeronautical communication?

• A. 400 MHz
• B. 243 MHz
• C. 118 MHz
• D. 2.4 GHz

Answer: (A)

In aviation, radio communications rely on fixed frequency ranges that are allocated for air-to-ground and air-to-air use. The standard voice comms between aircraft and ATC happen mainly in the VHF band around 118 to about 137 MHz. The UHF portion used for aviation-related communications runs up to the upper edge of around 400 MHz, with specific channels assigned for military or particular systems. Because of these allocations, a frequency at 400 MHz is not used for routine aeronautical communication. The other frequencies fall within the commonly allocated aviation bands: 118 MHz is a classic VHF air‑ground channel; 243 MHz lies in the UHF range used for certain aviation communications; and 2.4 GHz appears in some modern onboard systems or data links, not as the standard voice ATC channel.